The present invention relates to multi-platform communication systems and more particularly to a method and apparatus for providing an efficient and adaptive management of message routing in such communication systems.
Prior art net management solutions for management of message routing use techniques which require, one or more controller nodes or platforms, fixed a priori relay and routing assignments, and redundant transmissions.
The vulnerability of controller nodes to attrition, equipment failures, and electromagnetic countermeasures (jamming) make centrally controlled networks undesirable. Moreover, complex controller nodes must restrict their motion with respect to the remainder of the network community. Centrally controlled networks are critically dependent on links between the controller and its subsidiary platforms.
Fixed relay and routing assignments, either on the basis of time or frequency, prevent adapting to dynamic network connectivity changes and results in less reliable message delivery. Networks can vary because of: (1) changing populations due to new platform entries and exits or physical attrition and (2) changing connectivity due to platform motion, enemy jamming or transmission media disruptions. Rigid routing on the basis of frequency or time may also lead to a limited number of high density traffic patterns. Concentrated relay transmissions can lead to easier platform detection by intercept receivers and subsequent jamming will lead to large disruptions of network communications. Also, the overloading of a platform's terminal resources with non-adaptive redundant routing leads to underutilization of network capacity and, hence, increased message delay.
Excessive redundant transmissions should also be avoided because they not only consume precious channel capacity, but will result in increases in self-interference levels which will, in turn, reduce anti-jamming protection.
The foregoing has focused primarily on point-to-point communications in networks of low to medium connectivity which are typical characteristics, for example, of Army ground deployments. Other applications, for instance, Navy and Air Force communications, require, in addition, point-to-multipoint (multicast) routing, and in the limit broadcast routing. In these cases, a terminals transmissions are intended for a set of terminals or platforms performing the same or related warfare functions. In point-to-point routing, the broadcast nature of radio transmissions may create interference problems not encountered in wire networks. In point-to-multipoint routing, however, this broadcast capability can be used to advantage since multiple relays and/or destinations may be reached with a single transmission.
Repromulgation relay (flood routing) is a frequently used technique to perform a multicast routing. In this method, all terminals receiving a transmission for the first time retransmit it. Therefore, these transmissions propagate outwards from their originator until they reache all other terminals in the community, including all intended destination(s). This scheme is inefficient in terms of the number of transmissions it requires, significantly reducing system capacity. The inefficiency is greatest for networks with a high degree of connectivity.
Furthermore, in general, automated relay selection methodologies can be divided into two types: (1) geometric-based and (2) connectivity-based. The present invention focuses on the latter approach which uses exchanged connectivity information (identifying both one-way and two-way links) to make informed relay platform selections. The problem addressed in this scheme is, how can a (partial) knowledge of network connectivity allow a terminal to select relays for a message so that it can reach its intended destination(s)? In contrast, the problem addressed in geometric-based schemes is, without knowing terminal connectivity, what is the best way to assure reaching one or more intended destigations?
Geometric-based relay presumes relay suitability from position information (e.g. attitude and received position messages) and is most applicable to air platforms. Since there is no information on routes to destinations, coverage of the entire community is attempted. Message delivery is thus probabilistic. The cost of increasing this probability is increased message redundancy. However, the obtainable redundancy and reliability decrease as operational load traffic increases. The use of redundancy for relay reliability is an expensive use of system capacity. Redundancy also leads to increased circuit activation by non-circuit participant relays and hence, increased use of their terminal resources. This occurs because non-connectivity based relay assigns relay responsibility on a circuit rather than on an originator basis. Thus, it is possible that a set of relays which works for one originator will not work for another originator. There is no self-correction mechanism to modify the selection of relays. Also, relays are not aware of whether or not all originators are being relayed or if all destinations are being reached. FIG. 1 illustrates how a destination may not be reached if relays only share circuit responsibility and do not consider connectivity. As illustrated platform A and platform B share relay load for several circuits, but if platform A is assigned circuits on which platforms O and C are participants, platform C will not receive the originator's messages.
Other pitfalls of non-connectivity based relay schemes also are shown in FIGS. 2 and 3. Without considering link connectivity in each direction, it is possible that geometric types of criteria for selecting relays will not provide adequate performance in hostile environments. In FIGS. 2 and 3, platform A appears to be the best relay from its own perspective of comparative altitude and the number of incoming links. However, the presence of jamming on back links, or on links from source platforms to the intended relay, may negate the relay function. In FIG. 2 platform A, which has the highest altitude, receives messages from platforms B, C and D and appears to be in the best geometric position to relay between messages C and D. However, even though platforms A and B receive the same number of position messages, namely, three, the presence of jammers J and range attenuation break any connectivity from A to C or from A to D and leave relay B the only suitable relay between C and D. In FIG. 3, platform A appears to be a better relay than B or C by geometry, but because of jammer J, it cannot hear the originator's messages which it is supposed to relay. It should also be noted that geometric information cannot take antenna pattern directivity into consideration. Geometry does not necessarily imply connectivity.
A connectivity-based relay approach offers a significant enhancement over geometric-based schemes since both geometric factors, (e.g. range, altitude, obstructions, etc.), as well as terminal and jammer parameters, (e.g. transmit and receive power and antenna gains), are automatically considered in the assessment of link qualities in each direction.
Prior art approaches to network management solutions assume an established and static network based on frequency and/or time and determine how best to automatically route traffic between nodes (platforms).